[whatwg] Media queries, viewport dimensions, srcset and picture

[Markus Ernst]

Am 21.05.2012 07:49 schrieb Mike Gossmann:
> When all the picture vs srcset started showing up on twitter, I was initially behind picture. I'm sure you all know the arguments for it, and I liked those arguments. Today though, I was reading an article about the two, and there was a misunderstanding about how srcset was working in the comments, and it made me realize that something closer to srcset would be ideal.
>
> The big thing I realized is that as a developer, I do not want to write more media queries - or anything that works at all like them - into image elements. It's redundant. There's a good chance there's already a bunch of CSS in place controlling the shape and size of the image element itself, why should I have to write a bunch more, somewhere else, to control the src of the image too?
>
> Why can't it work so that in the html I say here's an image, there's a version of it at 150x150, and a version at 48x48, and then in the CSS I say that the image is 25% of the width of the article it's in, which works out to 100px wide, and then the browser can just decide that the 150x150 would be best, and scale it down. If I change the CSS, I don't have to change the html too, the images I provided are still only available at those sizes. With image/picture sources set by viewport dimensions, even something as simple as adding more padding around articles on a site could involve going through all the HTML and adjusting the breakpoints in the tags. This way layout, units, and screen dpi, don't matter when writing the HTML,
>
> I've seen people get confused and think srcset work this way, instead of by viewport size (unless I'm the confused one), and if they were right then srcset would work well for this. It would be even nicer if there was something even more CMS friendly, like:
>
> <img src="/img/people.jpg" sizes="100x200 300x250 900x300" pattern="/tools/resizer.php?img=people.jpg&width={w}&height={h}" alt="A picture of some people.">
>
> So src would be the fallback, then sizes would say which dimensions are available, in a fairly common format, using spaces to separate options like class does. pattern (probably a bad name) would be a template for the URL the browser can request the image from, replacing {w} and {h} with the requested dimensions. There wouldn't need to be a token for the dpi/resoultion/whatever, the browser could just request an image twice or three times or whatever the size. There's no point in having sizes="100x100 at 1 100x100 at 2 200x200 at 1" when you can just have sizes="100x100 200x200"
>
> This gives the designer/developer full control over the shape and size of the image element (through CSS), while still allowing the browser to make decisions based on bandwidth and whatnot.

I was actually writing a similar proposal and like the approach very 
much. I have 3 inputs on the pattern syntax:

1. @pattern needs some more variables so authors can use it without a 
server side handler, using distinct file names or directories or 
whatever, such as:
- directory path
- file name
- file name without suffix
- suffix

So patterns for use with src="/img/people.jpg" could also be e.g. 
(variable names are subject to optimisation...):
- /img/{filenameWithoutSuffix}_{w}x{h}.{suffix}
- /{dirname}/{w}x{h}/{filename}

2. It would be nice if @pattern defaulted to something that authors do 
all the time anyway. From my practice I suggest:
- /{dirname}/{filenameWithoutSuffix}_{w}x{h}.{suffix}

It is very easy to tell authors or even CMS page admins to use image 
file names such as people.jpg and people_200x300.jpg.

3. Variable syntax: Curly brackets are also used for variables by some 
server side template engines, such as PEAR HTML_Template_IT and 
HTML_Template_Sigma. These would replace or remove the @pattern 
variables. Thus, some other kind of variable delimiter might be more 
compatible.